RepeatedParamType should not be a subtype of anything (until ElimRepeated)

[adriaanm]

While looking at scala/bug#4775, scala/bug#8344, scala/bug#11015, I was thinking that T* should not be a subtype of Seq[T] (nor even Any, as it's not an expression type) until we've eliminated repeated params. This is important for overloading resolution (see referenced bugs).

Right? 🤔

[abgruszecki]

compat:scala2, since we reintroduce behaviour that was deemed a bug and removed in scala/bug#8344.

Some notes from me trying to fix this:

• overload selection sees Seq[X] @Repeated, which suggests to me that it happens post-ElimRepeated
• we cannot really special-case subtyping for Y @Repeated, since this is also the type of the argument inside the body of a function